Tesco finance director Laurie McIlwee has confirmed he is to step down after 14 years at the retailer.
The news comes ahead of annual results being published on April 16.
Tesco faced a period of "unprecedented change" in the supermarket industry, said McIlwee following the announcement.
"I am absolutely confident that Tesco will emerge from the current period of unprecedented change in the industry stronger than ever," he added.
He will remain in the position while the Tesco board searches for a new finance director.
Media reports speculated that Mr McIlwee had lost confidence in Tesco’s chief executive Philip Clarke’s plans to turn around the performance of the business.
According to analysts’ forecasts, the supermarket’s annual results, to be published on April 16, are predicted to reveal a 10% fall in profits.
Tesco's main rivals have also experienced falls in sales and profits as the discounters Aldi and Lidl grow market share.